Photographic emulsions containing carboxymethylated pigskin gelatin



United States Patent Ofi ice 3,184,312 Patented May 18, 1965 3,184,312 PHOTOGRAPHIC EMULSIONS CONTAMING CAR- 7 BOXYMETHYLATED PIGSKIN GELATIN John W. Gates, Jr., William G. Lovett, and Paul E. Miller,

Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Original application Nov. 14, 1958, S21. No. 773,837. Divided and this application Aug. 22, 1962, Ser. No. 218,509

1 Claim. (Cl. 96-94) This invention relates to the treatment of pigskin gelatin by an alkaline solution containing ammonium sulfate or acetate and by a carboxymethylating agent whereby the photographically undesirable impurities present therein are removed or deactivated and a product substantially corresponding in photographic properties to limed calf skin gelatin is obtained. The invention also relates to photographic emulsions which employ carboxymethylated pigskin gelatin as the carrier therein.

Pigskin gelatin as a rule exhibits high jelly strength, but the presence therein of certain impurities prevents its use as a carrier for silver halides in photographic emulsions, the use of gelatin for this purpose being mainly confined, at the present time, to calf skin gelatin and bone gelatin. When pigskin gelatins are used as the carrier in photographic emulsions for silver halide, such as silver chloride, silver bromide or silver bromoiodide there is, as a rule, considerable variation in photographic characteristics from one emulsion to the next. In general, the use of pigskin gelatin as the carrier in photographic emulsions results in desensitization of the coatings thereof when compared with emulsion coatings which used gelatins of the standard types. As pigskin gelatin usually exhibits substantial jelly strength, it seems as if it would be eminently suitable for photographic purposes except for the photographically active impurities which are found therein.

One object of our invention is to provide a pigskin gelatin useful photographically because of the absence of restrainers, desensitizers, or other photographically active impurities therein. Another object of our invention is to process pigskin gelatin to improve its photographic characteristics without any substantial detrimental effect on the jelly strength thereof. A further object of our invention is to provide a simple treatment of pigskin gelatin which converts that material to a form in which it exhibits photographic characteristics comparable to those of the calf skin gelatins and bone gelatins which are commonly used in the manufacture of photographic emulsions. Other objects of our invention will appear herein.

We have found that the photographic properties of pigskin gelatin may be markedly improved by applying certain refining steps thereto, which steps appear to remove the photographically active constituents of the pigskin gelatin. One of these steps involves the treatment in the cold of the pigskin gelatin with an aqueous alkaline solution containing ammonium acetate or ammonium sulfate. The amount of alkaline material employed is such that the pH of the mass is within the range of 8.510.5 and preferably within the range of 9-9.5. This alkalinity may for example be imparted by sodium carbonate, magnesium oxide, sodium hydroxide, potassium hydroxide, calcium hydroxide or the like.

The amount of sodium carbonate used would ordinarily be sufficient to impart a concentration within the range of 05-50%. The amount of magnesium oxide used is substantially an excess of that material which can be dissolved in water, as a saturated water solution of magnesium oxide ordinarily results in a pH on the order of 9. The amount of ammonium acetate or ammonium sulfate used gives a concentration thereof in the solution within the range of 220% or even more, being sufiicient to deter degradation of the gelatin being treated. Usually a 5% concentration of ammonium salt is useful.

The treating solutions may be made up in various ways. For instance, sodium sulfate and ammonia might be employed, but in that case a small proportion of sodium carbonate, magnesium oxide or the like should also be sup-. plied so that the non-volatile alkali is in excess of the sulfate ion or acetate ion content of the bath. The treatment of gelatin with alkaline material and ammonium salt may take place either prior to or after the carboxymethylation of the gelatin. Each of these steps are carried out at a chilled temperature (such as 40-60 F.) such that the gelatin remains in suspension in the mass rather than becoming dissolved therein.

The carboxymethylation of the pigskin gelatin is carried out at a pH within the range of 8.510.5, a pH of 9 being useful. Any of the alkaline materials referred to above for use in the leaching step of the invention may be employed in the carboxymethylation. The gelatin is treated with an amount of bromoacetic acid or chloroacetic acid (alpha-halo fatty acid) within the range of 220%, based on the weight of the gelatin, the reaction being carried out under chilled conditions (4060 F.) to avoid melting or dissolving of the gelatin in the liquid bath. Bromoacetic acid is preferred as the carboxymethylating agent, but other alpha-halo acids may be employed.

The pigskin gelatin which has been treated by the steps described is freed of restraining action when used as the carrier for silver halide in photographic emulsions which otherwise results in loss of speed of the pigskin photographic emulsion. By the treatment of the pigskin gelatin with the two steps outlined above, the restraining action thereof is reduced to such an extent that the gelatin has properties corresponding to those of the calf skin gelatins or bone gelatins which are commonly used as the carriers for silver halide in photographic emulsions.

Leaching of the pigskin gelatin is accomplished by first plumping the gelatin such as by holding in chilled water for a time and then adding alkali to adjust to the desired pH and ammonium acetate or ammonium sulfate.

Carboxymethylation of the pigskin gelatin is desirably kept to substantially the minimum which removes restraint to physical development. Bromoacetic acid is employed in an amount preferably within the range of 57%, based on the weight of the gelatin reacted upon. Magnesium oxide is a convenient alkali to employ therewith because the saturated solution thereof is at a pH suitable for the alkylation but low enough to keep hydrolysis to a minimum. Carboxymcthylation produces a gelatin having a low isoelectric point and free of any tendency to form slugs when mixed with gelatins from other stock sources and used in the preparation of photo Y graphic emulsions.

The following examples illustrate our invention;

Example 1 1,000 grams of pigskin gelatin was plumped in 12 liters of cold water for 30 minutes. 50 grams of magnesium oxide was added thereto and the mass was allowed" to stand for 30 minutes. A solution of 100; grams of bromoacetic acid in 1 liter of 'water'wasadded and the mixture was allowed to stand at 45 F. for .72 hours.

The resulting gelatin was w'ashedwith-Z changes of cold water and was then given one overnight and two 4-hou1' leaches in liters of water containing 0.5% sodium carbonate and 5% of ammonium acetate. vAfter washing for 3 hours in cold running tap water the aqueous gelatin V 710 was melted and its pH was adjusted to 5.7. The aqueous gelatin solution was mixed with carbon, filtered, chilled,

and dried in the usual'mannerr A carboxymethylated' pigskin gelatin was obtained having good photographic characteristics and free of impurities which would other-' Wise interfere with its useinphotographic emulsions.

Another like run was made except that 75 grams intead of 100 grams of bromoacetic. acid was used.-

. I Example 2 e V 200. grams of pigskin gelatin which had been given two 4-hour and l overnight leaches in water containing .5

sodium carbonate and 5%. ammonium acetate was washed, melted, treated with carbon, washed, chilled, and

dried. The gelatin was plumped 1 hour in 1 /2 liters of' cold water. grams of'magnesium'oxide was added andthe mass was allowed to stand for minutes.

40 grams of bromoacetic acid, dissolved in 500 cc. of 1 water was added and the mixturewas allowed to stand at 45 C. for 48 hours. 'The carboxymethylated gelatin thus obtained was washed in cold running water for 4 hours and the aqueous mass wasjmelted. After 'adjustmethylated gelatin had been used as the starting material the product could, after filtering, be sliced or otherwise divided and driedin the usual manner used in handling gelatin.

' Example 750 grams of pigskin gelatin was plumped in 7 liters of "tap' water. The gelatin was melted with water at 50 C., and the pH was adjusted to 9.5 by the addition of 20% sodium hydroxide solution. acetic acid dissolved .in 1 liter of water was added and solution was'stirred for 6 hours with the pH maintained '7 at 915. The pH was adjusted 00 5.7 with acetic acid,

ing the pH to 5.7, it was treatedlwith activated carbon, 1

filtered, chilled, and dried in a gelatin drying procedure."

A carboxymethylated pigskin gelatin free of photo.- graphically objectionable'impurities was obtained.

Example 3 Y A run similar-Example 2 was car ried out except that I 20 rather than 40 grams of bromoacetic acid was used. A carboxymethylated pigskin gelatin free; ,of photographically objectionable impurities wasiobtained; The

procedure was repeated but using 10 grams of bromoacetic acid. Similar results were obtained.

The following examples illustrate individual steps,

either leach steps or carboxymethylation steps to employ.

in processes of preparing .carboxymethylated pigskin gelatins having useful properties. Any of the leach steps described may be combined with one ofthe carboxy methylation steps in preparing the desired product.

7 Example 4 I 1500 grams of pigskin gelatin'was' plumped for /2 hour in a minimum of cold water. The plumped gelatin was leached for 3 hours twice and' once overnight in 15 liters of chilled water containing 88 grams of Na CO -H O and 750 grams of ammonium acetate. The gelatin thus obtained was washed 3 hours in 'chilledrunning water and was then melted. ;After adjusting the pH to 5.7-

the melt was treated with purifying carbon and it was then filtered and chilled. The gelatin obtained was then ready for carboxymethylation. If, however, the pigskin gelatin employed as the starting material had been previously carboxymethylated the gelatin, after chilling could be dried inthe usual manner for drying gelatin.

Example 5 and,-ll5 grams of purifying carbon was added. The

gelatiniwasfiltered, chilled,noodled, washed, and dried in the usual manner for handling gelatin or after chilling it is 'in ,a form wherein it can be subjected to theleach 'step'in accordance with'the methods described inExamples4and5.

Example 7 1500'grams of pigskin gelatin'leached as obtained by the methods of Examples 4 and 5 were plumped in 18 liter of cold tap. water'containing 56 grams of magnesium oxide and .112 grams of bromoacetic acid and themass was allowed to stand for 72 hours at F; The gelatin was washed for 4 hours in chilled running water, melted, the pH was adjusted to -5.7 by the" addition of acetic boxymethylated pigskin gelatin, however, does not show development restraint when employed in photographic emulsions; As an illustration, silver bromoiodide type emulsions were prepared and various gelatinswere added 950 grams of pigskin gelatin after plumping in cold water was given two 4-hour and 1 overnight cold leaches, each with 10 liters of tap water to which had been added 50' grams of, anhydrous sodium carbonate and 5Q0grams of ammonium sulfate. The leached gelatin was washed four hours'in chilled running water and was melted. After adjusting the pH to 5.7 the melt was treated with purifying carbon. The .gelatincould either be filtered,

chilled, and used in a carboxymethylation or if carboxy as 'is indicated in the table given. The carboxymethylated pigskin gelatins addedwere prepared by the methods described in Examples l'through 7 herein. The emulsion was prepared by first preparing the vsilver bromoiodide in dispersed form. The procedure described in Yutzy and Frame U.S. Patent No. 2,614,928having been used. The silver halide dispersion thus obtained. was mixed With the gelatin vehicle either'before or after sulfur and gold sensitization.

Theemulsion was optically sensitized with a cyanine dye. The film coatings obtained therefrom were exposed in an Eastman Type Ib Sensitometer for second and then processed for 5 minutes at 68 F. in Kodak Developer DK-SO. The speed values listed in the table are inversely proportional to the" exposure required to produce a densitygof 0.3 above fog.

Gelatin Identification Relative Gamma Fog Speed Bone Gelatin C0ntr0l 126 1. 38 11 Nontreated Pigskin Gelatin 1. 37 O7 Gelatin as made in Example 174 1. 5O 10 Gelatin as made in Example 2 151 1. 53 10 An alternative procedurefor preparing carboxymethylated pigskin gelatin which is. substantially free. of impurities which detrimentally affect the "photographic properties thereof involves carboxymethylation of the pigskin preliminary to the extraction .of gelatin there-. from. Thisprocedure involves the liming of the pigskin in which during atileast the majo-rfportion of the liming 56 grams of 'bromo-' operation bromoacetic acid or chloroacetic acid is supplied to the liming slurry. The gelatin extracted from the pigskin thus treated is eminently suited for use as a vehicle for silver halides in photographic emulsions.

The following example illustrates the preparation of carboxymethylated pigskin gelatin by the alternative procedure referred to:

Example 8 10 pounds of raw pork rinds were cold-limed for days with a slurry composed of 1.5 pounds of lime, 36 pounds of water and 120 grams of bromoacetic acid. At the end of this period, the lime slurry was drained off and the pigskins were washed for 2 hours. These rinds were then soaked at room temperature in 15 l. of Water containing 60 grams of sulfuric acid. The liquid was drained oil, the rinds were washed for 3 hours in cold water and drained. Acidification, washing and draining was repeated. The rinds thus obtained were extracted by covering with warm water and heating 3 hours at 140 F., with the pH being maintained at 4.5 to 5 .0 by the appropriate addition either of dilute sulfuric acid or of aqueous ammonium hydroxide. The raw gelatin solution thus obtained was separated from the rinds which were covered with warm water in lesser amount and a second extraction was carried out at a temperature of 150 C. The gelatin solution thus obtained was drained off and mixed with the first extract. The gelatin solution mixture was adjusted to a pH of 5.6 filtered, carbon treated, refiltered through a carbon filter and dried to obtain a carboxymethylated gelatin free of restrainers and desensitizers such as are ordinarily found in pigskin gelatins.

Example 9 10 pounds of raw pork rinds were degreased by extraction with a mixture of acetone and ligroin. These degreased rinds were soaked for one hour in cold water, the water was drained off and the thus plumped skins were limed for 5 days without application of heat using a slurry composed of 1.5 pounds of lime, 36 pounds of water, and 120 grams of bromoacetic acid. The limed rinds were soaked for 3 hours in cold water and were drained. These rinds were then soaked at room temperature in l. of water containing 60 grams of sulfuric acid. The liquid was drained off, the rinds were washed for 3 hours in cold water and drained. Acidification, washing and draining was repeated. The rinds thus obtained were extracted by covering them with 18 pounds of Warm Water and heating 3 hours at 140 F., and a pH of 4.6-4.9 maintained by adding either dilute sulfuric acid or dilute ammonium hydroxide, as is appropri ate. The extracted gelatin was decanted off and the residual stock was covered with 7 pounds of warm water and again extracted in a similar manner except at a 150 F. temperature. The second extract was combined with the first and the solution was filtered, carbon treated, refiltered with a carbon filter and dried.

The following data are for test performed on a highspeed bromoiodide emulsion chemically sensitized with sulfur and gold compounds. The films were exposed in an Eastman Type Ib Sensitometer for & second and were processed for three minutes in Kodak Rapid X-ray Developer. The speed values listed are inversely proportional to the exposure required to produce a density of 0.3 above fog.

The following examples illustrate methods for preparing carboxymethylated pigskin gelatins having good photographic properties.

Exwmple 10 11 pounds of raw pork rinds were limed at 72 F. for 7 days with a slurry composed of 1.8 pounds of lime, 40 pounds of water, 50.5 grams of chloroacetic acid and 7.0 grams of calcium hypochlorite. The lime slurry was then drained otf and the stock was washed for 2 hours The drained stock which had been prepared for extraction in the manner described was covered with 18 pounds of warm water and heated 3 hours at F, the pH being maintained at 5.0 by the addition of dilute sulfuric acid or of dilute ammonium hydroxide solution from time to time as needed. At the end of this time, the raw gelatin solution obtained was drained ofi and the stock was again covered with 9 pounds of warm wator for the second extraction, carried out in the same manner as described in the first extraction except that the temperature was maintained at F. At the end of this extraction the gelatin solution was drained off and combined with that from the first extraction. The pH of the solution was adjusted to 5 .6 and the solution was filtered, carbon treated and refiltered. The gelatin solution was dried by gelling at a lowered temperature, noodling and subjecting the noodles to a current of drying air having a low relative humidity until a mass of dry gelatin was obtained. The gelatin obtained was found to exhibit good jelly strength.

Example 11 11 pounds of raw pork rinds were limed at 72 F. for 7 days with a liming slurry of 1.8 pounds of lime, 40 pounds of water, 50.5 grams of bromoacetic acid and 7.0 grams of calcium hypochlorite. At the end of this period the lime slurry was drained off and the stock was washed for 2 hours.

The drained stock thus prepared for extraction was covered with 18 pounds of warm water and heated for 3 hours at 140 F., the pH begin maintained at 5 .0 over this period by the addition of either dilute sulfuric acid or dilute aqueous ammonium hydroxide as needed. At the end of this time, the raw gelatin solution was drained off and the stock was again covered with 9 pounds of warm water for the second extraction which was carried out in the same manner as the preceding, except that the temperatture was maintained at 15 0 F At the end of this extraction the gelatin solution was drained off and combined with the first extraction. The solution was adjusted to a pH of 5.6, filtered, carbon treated, and refiltered. The solution was then chilled and noodled and the noodles were subjected to a current of warm air of low relative humidity until a mass of dry noodles was obtained. There resulted a gelatin having good jelly strength.

The following data are for tests performed on a highspeed bromoiodide emulsion chemically sensitized with sulfur and gold compounds. The films were exposed in an Eastern Type 1b Sensitometer for second and were processed for five minutes in Kodak Developer DK-50. The speed values listed in the following table are inversely proportional to the exposure required to produce a density of 0.3 above fog.

This application is a divisional of abandoned applica tion Serial No. 773,837, filed November 14, 1958. 

